c#截取后台窗口的图片

         struct RECT

         {

             public int Left; // x position of upper-left corner

             public int Top; // y position of upper-left corner

             public int Right; // x position of lower-right corner

             public int Bottom; // y position of lower-right corner

         }

         public static Bitmap GetWindow(IntPtr hWnd)

         {

             IntPtr hscrdc = GetWindowDC(hWnd);

             RECT rect = new RECT();

             GetWindowRect(hWnd, out rect);

             IntPtr hbitmap = CreateCompatibleBitmap(hscrdc, rect.Right - rect.Left, rect.Bottom - rect.Top);

             IntPtr hmemdc = CreateCompatibleDC(hscrdc);

             SelectObject(hmemdc, hbitmap);

             PrintWindow(hWnd, hmemdc, );

             Bitmap bmp = Bitmap.FromHbitmap(hbitmap);

             DeleteDC(hscrdc);

             DeleteDC(hmemdc);

             return bmp;

         }

         //API声明

         [DllImport("user32.dll")]

         private static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);

         [DllImport("gdi32.dll")]

         public static extern IntPtr CreateDC(

                     string lpszDriver,        // driver name驱动名

                     string lpszDevice,        // device name设备名

                     string lpszOutput,        // not used; should be NULL

                     IntPtr lpInitData  // optional printer data

          );

         [DllImport("gdi32.dll")]

         public static extern int BitBlt(

          IntPtr hdcDest, // handle to destination DC目标设备的句柄

          int nXDest,  // x-coord of destination upper-left corner目标对象的左上角的X坐标

          int nYDest,  // y-coord of destination upper-left corner目标对象的左上角的Y坐标

          int nWidth,  // width of destination rectangle目标对象的矩形宽度

          int nHeight, // height of destination rectangle目标对象的矩形长度

          IntPtr hdcSrc,  // handle to source DC源设备的句柄

          int nXSrc,   // x-coordinate of source upper-left corner源对象的左上角的X坐标

          int nYSrc,   // y-coordinate of source upper-left corner源对象的左上角的Y坐标

          UInt32 dwRop  // raster operation code光栅的操作值

          );

         [DllImport("gdi32.dll")]

         public static extern IntPtr CreateCompatibleDC(

          IntPtr hdc // handle to DC

          );

         [DllImport("gdi32.dll")]

         public static extern IntPtr CreateCompatibleBitmap(

          IntPtr hdc,        // handle to DC

          int nWidth,     // width of bitmap, in pixels

          int nHeight     // height of bitmap, in pixels

          );

         [DllImport("gdi32.dll")]

         public static extern IntPtr SelectObject(

          IntPtr hdc,          // handle to DC

          IntPtr hgdiobj   // handle to object

          );

         [DllImport("gdi32.dll")]

         public static extern int DeleteDC(

          IntPtr hdc          // handle to DC

          );

         [DllImport("user32.dll")]

         public static extern bool PrintWindow(

          IntPtr hwnd,               // Window to copy,Handle to the window that will be copied.

          IntPtr hdcBlt,             // HDC to print into,Handle to the device context.

          UInt32 nFlags              // Optional flags,Specifies the drawing options. It can be one of the following values.

          );

         [DllImport("user32.dll")]

         public static extern IntPtr GetWindowDC(

          IntPtr hwnd

          );